The agency said infections had increased significantly among children ages 2 to 4.
Infections with the bacteria that causes walking pneumonia have risen significantly this year, particularly among young children, the Centers for Disease Control and Prevention warned this month.
The bacteria, called Mycoplasma pneumoniae, spreads through coughs and sneezes and can cause respiratory illnesses. Cases have risen among adults and children, but the most notable increase has been among children between 2 and 4, which experts say is striking given that the bacteria typically infects older children. Data suggests that doctors have diagnosed a growing number of children in this age group with infections after they sought treatment in emergency rooms for pneumonia.
Despite its name, only around 10 percent of people infected with Mycoplasma pneumoniae actually develop pneumonia, which is a type of lung infection. When the bacteria does cause pneumonia, it tends to be milder than other forms of the illness, which is why it’s called “walking pneumonia.” Still, it can cause a fever, chest pain and other symptoms that persist for weeks, and in rare cases can lead to hospitalization.
There are roughly two million infections with the bacteria each year in the United States, according to C.D.C. estimates. That number is most likely an undercount, though, since many cases are not diagnosed.
Cases seem to be dipping after peaking in late August, but the C.D.C. said it isn’t yet clear whether that decrease will last, and said that people should stay alert to potential symptoms of an infection.
“Providers should be on the lookout for it, and the general public — and especially parents,” said William Edens, lead of the Legionella and atypical pathogens team at the C.D.C.